8 Plants. Chapter. Structure and Function. Chapter Preview. ) plant allow it to grow and

Transcription

1 Chapter 8 Plants Structure and Function How does the structure of a ) plant allow it to grow and reproduce? Chapter Preview O The Plant Kingdom Discover What Do Leaves Reveal About Plants? Active Art Plant Ceil Structures Analyzing Data Water Loss in Plants Without Seeds Discover Will Mosses Absorb Water? Try This Examining a Fern Skiffs Lab Masses of Mosses O The Characteristics of Seed Plants Discover Which Plant Part Is It? Try This The In-seed story Skills Activity Calculating O Gymnosperms and Angiosperms Discover Are All Leaves Alike? Try This The Scoop on Cones Active Art The Structure of a Flower Math Skills Multiples Skills Lab A Close Look at Flowers O Plant Responses and Growth Discover Can a Plant Respond to Touch? At-Horne Activity Sun Seekers 248 The Passiflora plant produces delicate, highly scented flowers.

2 Chapter DI R ouerj CHANNEL OOL Seed Plants Video Preview Video Field Trip Video Assessment Lab zonechapter Project Design and Build an Interactive Exhibit Cotton, medicines, and paper are just some of the products that come from plants. Which plants are the sources of these products, and how are the products made? In this project, you will build an exhibit to teach young children how a plant becomes a useful product. Your Goal To build an interactive exhibit showing how a particular plant is transformed into a useful product To complete this project successfully, you must o choose one plant product and research where it comes from e design an interactive exhibit that shows how the product is made o build your exhibit and ask some children to critique it o use the children's feedback to redesign your exhibit e follow the safety guidelines in Appendix A Plan It! Think of a creative way to teach children about the plant product you chose. Then sketch out your exhibit design and obtain your teacher's approval to build it. Also, identify a few children who can provide you with useful feedback.

3 The Plant Kingdom Reading Preview Key Concepts What characteristics do all plants share? What do plants need to live successfully on land? How do nonvascular plants and vascular plants differ? What are the different stages of a plant's life cycle? Key Terms cuticle vascular tissue zygote nonvascular plant vascular plant sporophyte gametophyte Target Reading Skill Building Vocabulary A definition phrase by telling about its most important feature or function. After you read the section, reread the paragraphs that contain definitions of Key Terms. Use all the information you have learned to write a definition of each Key Term in your own words. zone What Do Leaves Reveal About Plants? 1. Your teacher will give you two leaves from plants that grow in two very different environments: a desert and an area with average rainfall. 2. Carefully observe the color, size, shape, and texture of the leaves. Touch the surfaces of each leaf. Examine each leaf with a hand lens. Record your observations in your notebook. 3. When you have finished, wash your hands thoroughly With soap and water. Think It Over Inferring Use your observations to determine which plant lives in the desert and which does not. Explain. There are some very strange plants in the world. There are plants that trap animals, plants that bloom only once ev thirty years, and plants with flowers that smell like rotting meat. You probably don't see such unusual plants every day. But you probably do see plants every day. You encounter plants whenever you see moss on a tree trunk, run across a lawn, pick ripe tomatoes from a garden. And all plants, both the unfamiliar and the familiar, have a lot in common. What Is a Plant? Members of the plant kingdom share several characteristics Nearly all plants are autotrophs, organisms that produce their own food. All plants are eukaryotes that contain many cells. In addition, all plant cells are surrounded by cell walls. Plants are autotrophs. You can think of a plant as a sunpowered, food-making factory. Sunlight provides the energy for this food-making process, photosynthesis. You don't need a microscope to see plants because they are multicellular. Like many other multicellular organisms, plant cells are organized into tissues. Recall that tissues are groups of similar cells that perform a specific function. Plants vary greatly in size. Both the tiniest moss and the tallest tree are plants.

4 4 Plant cells Go Online active ar For: Plant Cell Structures activity Visit: PHSchool.com Web Code: cep-1041 If you were to look at a plant's cells under a microscope, you would see that plants are eukary- Otes. But unlike the cells of some other eukaryotes, a plant's cells are enclosed by a cell wall. Within a cell are chloroplasts and a vacuole, which is a large storage sac for water, wastes, food, and other substances. Adaptations for Living on Land Blost plants live on land. How is living on land different from living in water? Imagine multicellular green algae floating in the ocean. The algae obtain water and other materials directly from the water around them. The water holds their bodies up toward sunlight. When algae reproduce, sperm cells can swim to egg cells. Now imagine plants living on land. What adaptations must they have to meet their needs without water all around them? For plants to survive on land, they must have ways to obtain water and other nutrients from their surroundings, retain water, transport materials in their bodies, support their bodies, and reproduce. Obtaining Water and Other Nutrients Recall that all organisms need water to survive. Obtaining water is easy for algae because water surrounds them. To live on land, though, plants need adaptations for obtaining water from the soil. Plants must also have ways of obtaining other nutrients from the soil. Reading Why is obtaining water easy for Checkpoint / algae? Cell wall Chloroplast membrane Vacuole Nucleus A Single plant cell FIGURE 1 Plant Cell Structures Like all plants, this maple tree is multicellular. Plants have eukaryotic cells that are enclosed by a cell wall. Relating Diagrams and Photos Which cell structures can you see in the inset photograph of plant cells? Chapter 8 251

5 1 Retaining Water Plants must have ways of onto the water they obtain. Otherwise, they could dry out due to evaporation, IVhen there is more plant cells than in the air, the water leaves the plant enters the air. One adaptation that helps a plant red water loqs is a waxy, waterproof layer called the u tic!' that covers the leaves of most plants. Materials A plant needs to tramp, Transporting water, minerals, food, and other materials from part of its body to another. In general, water and als are taken up by the bottom part of the plant, food is made in the top part. But all of the plant's need water, minerals, and food. In small plants, materials can simply move from cell to the next. But larger plants need a more efficient way to transport materials farther, from one part plant to another. These plants have transport tissue called vascular tissue. Vascular tissue is a system tubelike structures inside a plant through which minerals, and food move. Support A plant on land must support its own bod It's easier for small, low-growing plants to suppor themselves. But for larger plants to survive, the plants food-making parts must be exposed to as much sun. light as possible. Rigid cell walls and vascular tissue strengthen and support the large bodies of these plants. Reproduction All plants undergo sexual reproduction that involves fertilization, the joining of a sperm cell with an egg cell. The fertilized egg is called a zygote. For algae and some plants, fertilization can only occur if there water in the environment. This is because the sperm of these plants swim through the water to the egg cells Other plants, however, have an adaptation that makes it possible for fertilization to occur in dry environments. Reading Checkpoint Why do plants need adaptations to prevent water loss? 252 FIGURE 2 Transport and Support For this tall coconut palm to survive, it must transport water, minerals, and food over long distances. It must also support its body so its leaves are exposed to sunlight.

6 Math Analyzing Data Water Loss in Plants The graph shows how much water a certacn plant loses during the hours shown. Reading Graphs What variable is plotted along each axis? 2. Interpreting Data According to the graph, during what part of the day did the plant lose the most water? The least water? 3. Drawing Conclusions What could account for the pattern of water loss shown? 4. Predicting How would you expect the graph to look from 10 P.M. to 8 A.M.? Explain your reasoning e 180 o Plant Water LOSS 8 AM 10 AM Noon 2 PM 4 PM 6 PM 8 PM 10 PM. Time of Day Classifying Plants Hundreds of thousands of plant species exist in the world today. scientists informally group plants into two major groups - nonvascular plants and vascular plants. Nonvascular Plants Plants that lack a well-developed system of tubes for transporting water and other materials are known as nonvascular plants. Nonvascular plants are lowgrowing and do not have roots for absorbing water from the ground. Instead, they obtain water and materials directly from their surroundings. The materials then simply pass from cell to cell. This means that materials do not travel very far or very quickly. This slow method of transport helps explain why most nonvascular plants live in damp, shady places. Most nonvascular plants have only thin cell walls to provide support. This is one reason why these plants cannot grow more than a few centimeters tall. Vascular Plants Plants with true vascular tissue are called vascular plants. Vascular plants are better suited to life in dry areas than are nonvascular plants. Their well-developed vascular tissue solves the problem of transport, moving materials quickly and efficiently throughout the plant's body. Vascular tissue also provides strength, stability, and support to a plant. Thus, vascular plants are able to grow quite tall. Chapter 8 253

7 Rock containing two plant fossils FIGURE 3 Ancient and Modern Plants scientists understand the origin of plants. These fossils are of two plants that lived about 300 million years ago. Notice the similarities between the fossils and modernday horsetails (above) and ferns (top right). organisms were the origin of plants biologists studied today's plants? In search of answers, the traces of ancient life forms preserved in rock and other stances. The oldest plant fossils are about 400 million years The fossils show that even at that early date, plants already many adaptations for life on land, including vascular tissue Better clues to the origin of plants came from comparing chemicals in modern plants to those in other organisms. In ticular, biologists studied the green pigment chlorophyll, found in the chloroplasts of plants, algae, and some bacteria Land plants and green algae contain the same forms of This evidence led biologists to infer that ancient green algae the ancestors of today's land plants. Further comparisons of genetic material clearly showed that plants and green algae very closely related. In fact, some scientists think that green algae should be classified in the plant kingdom. Reading Checkpoint What are the most likely ancestors of today's plants? Complex Life Cycles Plants have complex life cycles that include two different stages, the sporophyte stage and the gametophyte In the sporophyte (SPOH ruh fyt) stage, the plant produces spores, tiny cells that can grow into new organisms. A spore develops into the plant's other stage, called the gametophyte. In the gametophyte (guh MEE tuh fyt) stage, the plant produces two kinds of sex cells: sperm cells and egg cells. Figure 4 shows a typical plant life cycle. A sperm cell and egg cell join to form a zygote. The zygote then develops into a sporophyte. The sporophyte produces spores, which develop into the gametophyte. Then the gametophyte produces sperm cells and egg cells, and the cycle starts again. The sporophyte of a plant usually looks quite different from the gametophyte. Reading Y Checkpoint During which stage does a plant produce spores? 254

8 FIGURE 4 plant Life Cycle plants have complex life cycles that consist of tvvo stages the sporophyte stage and the gametophyte stage. Interpreting Diagrams During which stage are sperm and egg cells produced? Sporophyte Stage Produces spores Fertilization produces a zygote Gametophyte Stage Produces sperm cells Produces egg cells Sperm cells Egg cells Section 1 Reading Skill Building Vocabulary Use your sentences to help you answer the questions below. Reviewing Key Concepts I. a. Listing List three characteristics of plants. b. Comparing and Contrasting Describe three ways that plant cells differ from the cells of some other eukaryotes. c. Predicting How might a plant cell be affected if it lacked chloroplasts? 2. a. Identifying What are five adaptations that plants need to survive on land? b. inferring M Ṭ hy is a cuticle a useful adaptation in plants but not in algae? 3. a. Reviewing How do vascular plants differ from nonvascular plants? b. Explaining Explain why vascular plants are better suited to life in dry areas. c. Classifying Would you expect a tall desert plant to be a vascular plant? Explain. 4. a. Describing What are the two major stages of a plant's life cycle? b. Sequencing Describe in order the major events in the life cycle of a plant, starting with a zygote. Writing in Science Video Script You are narrating a video called Living on Land, which is written from the perspective of a plant. Write a one-page script for your narration. Be sure to discuss the challenges that life on land poses for plants and how they meet their needs. Chapter8 255